The present invention relates to a process for the manufacture of temperature-sensitive polymers utilizing a heat transfer fluid comprising a hydrocarbon fluid selected from aliphatic hydrocarbons, alicyclic hydrocarbons, aliphatic- or alicyclic-substituted aromatic hydrocarbons, or mixtures thereof, the hydrocarbon fluid having a boiling point from 220° C. to 250° C. and a melting point less than 40° C. The present invention further relates to a process for manufacturing temperature-sensitive polymers utilizing a heat transfer fluid comprising a fluid selected from phenylcyclohexane (also known as cyclohexylbenzene), bicyclohexane (also known as bicyclohexyl), hydrogenated biphenyl having a level of hydrogenation between phenylcyclohexane and bicyclohexane, or mixtures thereof. The present invention further relates to plastic products made in accordance with the inventive process.
Heat transfer fluids, which can also be termed “heat carriers”, are used to transfer heat energy between systems of different temperatures. Heat transfer fluids generally are eminently well-known and have been used commercially for a long time. The large majority of commercial transfer fluids, including Therminol®VP-1, (Solutia Inc.), Diphyl®DT (Bayer A.G.), Dowtherm®A (Dow Chemical) and Therm® S300 (Nippon Steel), all consist of a binary system of about 26% biphenyl and 74% diphenyloxide. Such heat transfer fluids are characterized by a boiling point of about 256° C. at atmospheric pressure and, in addition, exhibit desirable in-use properties including oxidative and thermal stability, good heat transfer properties, virtually no equipment corrosion and good economy. Irrespective of such benefits, boiling temperatures of commercial heat transfer fluids, generally above 250° C., are too high for the manufacture, including extrusion, of temperature-sensitive polymers, such as Nylon 6 and PTT (polytrimethylene terephthalate), and can lead to difficulties in the processing of the polymer and, consequently, undesirably altered in-use properties of the extruded article. In fact, a boiling point difference exceeding about 2° C. can lead to a different crystallization behavior of the polymer in the extruded article and thus yield an article exhibiting modified bulk and surface characteristics. The problem had been known for a long time and no completely satisfactory commercially-viable approaches, e.g. heat transfer fluids meeting essentially all the desired performance properties, for eliminating the difficulties have been made available up to now.
Polymer manufacturing temperatures exceeding about 245° C., can be detrimental to the quality of the extruded article made from temperature-sensitive polymers. The lowering and control of the boiling temperature of heat transfer fluids was normally achieved by applying partial vacuum. However, the use of reduced pressures requires supplementary equipment and, more importantly, selected pressures can, and normally will, vary considerably during industrial polymer manufacturing operations to thus yield deficient polymer articles. The prior art relating to the manufacture of extruded polymer articles, and the use of heat transfer fluids in such an arrangement, is well-known in the relevant technical community. U.S. Pat. No. 3,925,013 teaches the use of binary and ternary eutectic solvent mixtures for use in disperse dye carrier formulations to improve handling properties at ambient temperatures. A binary mixture of from 55–10% biphenyl and 30–45% naphthalene was found to possess a suitably lowered crystallization point so that dye carrier properties become easier. U.S. Pat. No. 5,397,491 describes heat transfer fluids, containing substituted diphenyl, exhibiting improved thermal stability at temperatures exceeding 300° C. JP-A-9145994 describes heat transfer fluids based on mixtures of alkyl naphthalenes and alkylbiphenyls, particularly combinations of diethyl biphenyl and diisopropyl naphthalene. WO 8907634 pertains to heat transfer agents consisting particularly of diphenylethers of terphenyl, biphenyldiphenyl ethers and naphthalene diphenylethers. JP-A-6968314 discloses heat transfer agents containing mixtures of biphenyl and/or naphthalene and diphenylether and terphenyl. WO 98 50483 concerns heat transfer fluids exhibiting favorable thermal stability comprising a mixture of tetrahydro(phenylethyl)naphthalene and dibenzyl toluene.
PCT Application no. PCT/EP00/12077 discloses a process for manufacture of temperature-sensitive polymers using a heat transfer fluid consisting essentially of a binary mixture of biphenyl and naphthalene in a weight ratio of 65:35 to 55:45. While this fluid is a stable and efficient heat transfer fluid with a boiling point below 245° C., it is desirable to provide a heat transfer fluid that meets more of the desired heat transfer fluid properties.
It is desirable to provide a heat transfer fluid useful for the manufacture of temperature-sensitive polymers having a lower boiling point and lower melting point than currently available heat transfer fluids, which preferably also has improved environmental, safety and health properties.
It has now been discovered that a heat transfer fluid selected from a hydrocarbon fluid selected from aliphatic hydrocarbons, alicyclic hydrocarbons, aliphatic- or alicyclic-substituted aromatic hydrocarbons, or mixtures thereof, the hydrocarbon fluid having a boiling point from 220° C. to 250° C. and a melting point less than 40° C., achieves these desired properties, and meets the demands for use in the production of temperature-sensitive polymers.
It has now been further discovered that a preferred heat transfer fluid selected from phenylcyclohexane, bicyclohexane, hydrogenated biphenyl having a level of hydrogenation between phenylcyclohexane and bicyclohexane, or mixtures thereof achieves these desired properties, and meets the demands for use in the production of temperature-sensitive polymers.